vaillb



(No Model.) 2 Sheets-Sheet 1.

P 0.- VAILLE. TELEPHONE EXCHANGE SYSTEM.

No. 262,261. Patented Aug. 8, 1882.

2 iv 357v 2 5 ($231. J hJ'f'e'd'cb' a ul Z Inn/e 77 260 r PETERS.Pmw-umn mn. Wahin m. o c

(No Model.) 2 SheetsSheet, 2.

I. O. VAILLE. TELEPHONE EXCHANGE SYSTEM. No. 262,261. Patented Aug. 8,1882.

771a gro 60.

Battery.

V/Qnsses. Invefifior fl, w0 maka; Wm

UNTTED STATES PATENT @EETEE.

TELEPHONE-EXCHANGE SYSTEM.

SPECIFICATION forming part of Letters Patent No. 262,

261, dated August 8, 1882,

Application filed May 10, 1882. No model.)

To all whom it may concern Be it known that I, FREDOK. O. VAILLE, ofDenver, in the county of Arapahoe and State of Colorado, have inventedcertain Improvements in Telephone- Exchange Systems, of which thefollowing is a specification.

This invention relates more especially to an organization'of electriccircuits and apparatus known as a telephonic exchange system, wherebydirect intercommunication can be established over telegraph or telephonelines-extending in different directions from a central station orexchange between a number of separate sub-stations situated at variouspoints within the geographical district which the central station isdesigned to serve. In an organization of this character the arrangementof the lines, commutators, and apparatus in the exchange or centralstation is such that any two sub-stations within the district may at amoments notice be placed in direct telegraphic or telephoniccommunication by the act of an operator or attendant, who is keptconstantly on duty at the central station, and who, upon being notifiedto do so by a subscriber or other person at a sub-station, unites theterminals of the two lines which are desired to be connected together bymeans of suitable switching or connecting devices provided for thispurpose.

In every central telephone-station there are a certain numberof specificand distinctoperatious,which must necessarily be performed, and certaininstrumentalities are requisite for the accomplishment of suchoperations. Itisnecessary to provide devices for the proper reception ofsignals from the several sub-stations. It is necessary, also, to arrangefor the intercommunication of different circuits and provide apparatusto that end. It is constantl found necessary to signal the differentsub-stations, this operation also requiring special mechanism. We mustalso be able to supervise the entire operation, that we may assist thesub-stations to understand oneanother, disconnect them when they havefinished conversation, and, ifthey so desire, furnish them with a secondcorrespondent. function apparatus must To accomplish this be arrangedwhereby the central-station telephones can be rapidly and convenientlybrought into communication with any circuit or with any two linesentering the central station.

To so combine the various circuits and instrumentalities requiste thatthe several operations hercinbetore enumerated shall be promptly,conveniently, and, in a great measure, antomatically accomplished, whileat the same time the precision and correctness of each special operationis insured, is the object of my invention.

To this end my invention consists in the entire separation of thefunctions of the central station from one another, so that signals arereceived by one set of operators, circuits are interchanged and combinedby another, and connections supervised, signals transmitted, anddisconnections made by a third.

It further consists in the specific arrangement of certain devices,whereby a signal received at the central station from any sub-stationplaces the line over which it is received into direct communication withthe centralstation telephones without breaking its original circuit, andwhereby the connection of any two circuits, by means of a switch-boardconnection-strip, automatically notifies the supervising operator thatsuchaconnection is made and simultaneously causes a call-signal to betransmitted to each of the two lines so connected, or, in the event ofbut one line being changed from its normal position to theconnecting-strip, a signal is sent over that line alone, the supervisingoperator still being notifled.

It further consists in certain instrumentalb ties and circuits, wherebyany two circuits,

when combined for intercommnnication, re-

main at all times in communication with the central station. 4

It consists also in devices whereby the operator or attendantsupervising any connection is enabled at all times to know the precisecondition of the switch-board with reference to all substation linesconnected.

In the accompanying drawings, Figure 1 is a diagram illustrating theorganization of a central or exchange station, showing the relations ofthe Various each other and illustrating the method of operation. Fig. 2is a side elevation of an annunoiator having its electrical connectionsarparts of the apparatus to "anged in accordance with my invention.Figs. 5, 4, 5, and 6 are diagrams showing the relationofthcsupervising-switch to the main switch and connected circuits atditferent periods during the time of connection.

teferring to Fig. 1, L, L, L L, L", and L represent a series ofline-wires, each connected atthe central station with the mainswitchboard B (which may be of any desirable form of construction) atthe points indicated by the small numerals 1 2 8 4, &c., binding-screwsof course being the practical means adopted for such attachment. Eachwire extends to one or more sub-stations, each of which may bedesignated, for the sake of brevity and convenience, by any desiredspecific numbers, as shown. At the distant end of each sub-station lineare placed, in a manner well understood, a signal-bell and electricgenerator, by which signals may be both received and transmitted,together with a receiving and transmitting telephone. All these devicesand their-arrangement at the sub-station in connection with the line arewell known,-and therefore do not require detailed description. Theseveral lines 11, after reaching the central-station switchboard,continue, by means of the vertical strips or bars of metal 1 2 3, overthe face of the board and terminate normally, after passing throughtheir respective annunciators 0, in a common ground-wire, s. Theconnection of each annunciator will be made plain by ret'erence to Fig.2. It will be seen that the metal bar or strip ends at the lower edge ofthe switchboard, but makes contact normally by means of the plug 7 witha metal plate, 19, which is, through the intervention of the wire a andthe branch wire a, connected with one terminal of the annunciator-helixO, the other terminal wire of which is connected by the wire a with theground-plate 8.

To accomplish a certain specific result, which will be hereinafter mademanifest, l permanently connect a branch wire, 0), as shown in Figs. 1and 2, with the main annnnciator-wire a at the point 00, which mustinvariably be at the line or outer side of the annunciatorcoil, andattach the other end of the same to the metal base D of the annunciator.This branch ordinarily has no eii'ect at all on the electrical conditionof the line; but when a call signal is sent from a sub-stationtheimpulse passing through the annunciator-magnet energizes the same,causing the attraction of its armature. The drop or shutter 0 is thusreleased and falls upon a support or anvil, t, which is formed of metaland is common to all the drops of the series. This is connected by aconducting-wire, t, with the main stem of a key or press-button, F,contacting by its own resiliency with a back-limit plate or bridge, to,this again being connected by wire g with an electro-magnetic signaling;device, Vsucli as a magnet provided with a vibrating armature-and thencethrough wire 9, armature Gr, limit screw It, and wire to some generator-or source of electricity, H, which may be a batas shown or, if founddesirable, wire be branched from the main magneto and pole-changer ofthe tery, may generator or battery exchange.

Immediately below the key or press-button F is a metal plate, 10, uponwhich the said key makes contact when pressed, contact with the bridgebeing simultaneously broken. The plate is attached to a wire, y, leadingto a receiving-telcphone, T, and transmitter L, and thence to the earth.The whole of this receiving apparatus is for convenience placed on tableE.

Attached to the common contact bar or anvil t is a wire, q, whichconnects the same with a button-switch, V. This is used to connect ordisconnect a second switch-board, which, it used, may be placed side byside with the first one. \Vhen the switch V is placed on the button jthe drops of the adjoining section, (not shown,) although falling upontheir own anvil, are in electrical connection 'with the instruments ontable E. This arrangementmay be extended so far as may be founddesirable, each section being provided with a buttonswitch, V, by whichthey may each work with their own receiving-instruments or may beswitched together by the switch V, to theend that when desired oneoperator at table E can respond to the calls ot' all the sections. Theconnecting-plugs r of the linecircuits 1 to L and 9 and 10 are shown asbeing withdrawn from their ordinary places, and as being in use upon theface of the board in the act of connecting various substation lines.Those belonging to the lines 5 to 8, inclusive, are still in theirplace.

For distinction, 1 herein call the switch-board B the main switch, as toit all the main lines run. At any convenient place near the said mainswitch B, I locate a second switch-board, A, which I call thedisconnection-board. It is notnecessary that this board A shall havemore than four horizontal conductingstrips, 7., l, m, and it. Itsvertical conductingstrips or bars, a toj, however, must be equal innumber to the horizontal connecting-strips a b c d cfot' the main board.I place an annunciator-drop, 0, immediately below each oi; the saidvertical conducting-bars a. l) c, and connect the helices of theelectro-magnets of the said annunciator-drops each on one side with itsown vertical strip and on the other with separate wires Z, leading fromthe horizontal bars a b c of the main switch B, so that the strip a, forexample, of the switch B is metallically connected by the wire Z and theannunciator-coil o with the vertical strip a of the disconnecting-switchA. By thus interposing the drop 0 between the vertical strips of theswitch A and the horizontal strips of the switch B any communicationpassing between the two switches must necessarily pass through the drop0 and cause it to fall. The interposition of the resistance of theannunciator-coil at this point also subserves another purpose, whichwill hereinafter appear.

The connecting-plugs rofthe disconnectingboard B, (whichmay be of anydesired construction, inasmuch as their only function is to establishcontact between the upright and cross bars of the switch,) all normallyrest on the upper cross-bar, k, in which position seven of the plugs areshown, so that in a state of rest, when none of the sub-station linesare connected together for intercommunication, all the plugs r arearranged in a row, connecting all the upright strips a b c with thecross-strip k. To this eross-stripkis attached a conducting-wire, k,leading through an electro-maguetic alarm-which may be of any desiredconstruction, although I prefer a signaling instrument of the classtechnically known as buzzers-to an electrical generator, M, which maybea magneto or dynamo electric machine, as shown, or, if preferred, may bea voltaic battery, having its current thrown into waves ofalternatingdirection by an automatic pole-changer. The other pole ofthe generator Mis connected with the earth by the wire l Thus, when all the plugs r areon the switchbar It, all the horizontal strips or I) c of the mainswitch B are virtually "open terminals of a charged electric circuit,which, commencing at the earth, may be traced over the wire l generatorM, wire Z buzzerI, wire k, horizontal strip k, plugs r, thence via allthe upright strips of the board A, the connecting-wires Z, and thehorizontal bars or strips a b cot' board 13. I will here mention that ifthe generator M is a magneto ordynamo machine it must be kept in rapidrotation by a constant power.

Since the horizontal strips of switch B are each normally insulated fromone another and have no electrical connection with any conductor, it isobvious that though they are constantly charged by the electricity fromthe generator M, no result can accrue from such a state of charge untilthe circuit is closed by causing one or more of the said horizontal barsto make contact with some conductor leading to the earth. When one ofthe plugs 1 on the main switch B is removed from its ordinary socket andplaced attheintersection ofany ofthe cross horizontal strips with itsown upright strip, the circuit of the generator is completed, and asuccession of electrical pulsations are transmitted over the line to thesub station, there ringing the bell and giving the signal. If two plugsare at once placed on the same strip, the current divides, half going toone sub-station and half to the other. In the drawings I have shown theplugs r of the circuits 1 and 2 placed on the-horizontal bar cot theswitch. Thus the circuit of the generator is closed cm the plug r, stripa, wire Z, horizontal bar 0, plugs r, on lines 1 and 2, and to ground atthe distant sub-station, and thus, by the simple act of moving theplugs, the alarm is automatically given at the sub-stations, the maingenerator-circuit bifurcatiu g at the two plugs on the bar 0, and

the circuit being formed as graphically shown in the diagram Fig. 3, inwhich N N represent the sub-stations connected by their respectiveline-wires with the main switch-board B, the plugs r 1' making aconnection of both lines by means of the wire a through an annunciator,0, with the switch-board A at the uppermost hori. zontal strip, andthence by the connecting-wire tothemagneto-generator. Furthermore,astheannunciator o is included in the new circuit thusformed,itsmagnetisenergizedanditsshutter dropped, giving to thesupervising operator the intelligence that two lines are connected andon that strip. It is clear that placing any of the plugs r on any of thecross-strips a b 0 will produce the same result, so long as thecorresponding vertical strip on the disconnecting-switch has its plug 1"on the generatorstrip k. The second bar, I, of the disconnecting-switchA is permanently connected by a wire, Z, with the earth direct. When anytwo sub-station lines are completely connected together, andconversation has commenced, the plug 1", belonging to the upright stripwhich represents on the disconnecting-board the horizontal strip whichconnects the said two lines, is moved down to the second bar, I. Thisservesa double purpose. The supervising operatoris thus, by the positionof the plug, apprised that the two lines are connected and thesubscribers conversing, and by such an arrangement, moreover, thetwolines connected are throughout the conversation maintainedincommunication with the central station through the annuncitor-drop 0.Although this is a steady leak to earth, the resistance of theannunciator-coil prevents the leakage of so much electricity as wouldtend to materially diminish the sound.

In the drawings the line-strips 3 and 9,connecting the sub-stations 213and 84:, are in the described position, the plugs 1" are placed on thestrip cl, that being connected by wire Z, annunciator o, strip (1', plug1", with strip Z, wire I, and ground. I have also shown this position indetail in the diagram, Fig. 4.

To the third horizontal strip, at, is attached a connecting-wire, m,leading to a switch, J, which in this case I have shown as a strapkeymaking normal contact with a bridge, 10 leading to transmitting andreceiving telephones L T, and thence to earth. Just below the key is afront contact, m connected with a wire, which branches from thegeneratorwire 1 The functions of these devices are as follows: When itis necessary for the supervising operator to speak to either or bothsubstations of two connected lines the plug 1" is slid down and placedon the third strip, m, thus placing the telephones L T in branch circuitwith the two connected lines in precisely the same manner as the twoforegoing operations are performed.

Switch-bars 4 and 10, connecting sub-sta-' tions 79 and 68, are shown inFig. l as being so arranged, while Fig. 5 is a diagrammatic detail ofthe same position. The key and front contact connected with thegeneratorbranch I provide, so that if either sub-station fails torespond to the automatic ring, and the operator on listening ascertainssuch failure, he may easily give a second call-signal by pressing thekey instead of again moving the plug 1". I may, if I so desire, use atwo-point button-switch instead of the key.

The fourth bar, '11, connects by wire a with a battery, K, of sufficientstrength to operate the annunciator when connected with one or moresubscribers lines. When by occasional listening a conversation isascertained to be concluded, or when a subscriber rings off, and thusdrops the annunciator o, the supervising operator will at once place theplug 0" on the lower bar, a. The circuit of the battery K, which hashitherto been open, is thus closed through to the terminal sub-stationsof the connected lines. The magnet of the annunciator 0 consequentlybecomes active, and the armature is attracted, releasing the drop, andit is then found impossible to replace the drop so long as the circuitof the battery is thus closed. The situation is shown in diagram by Fig.6. The operator then passes an order to the switchman to disconnect thetwo lines, and not until both lines are accordingly disconnected is thecircuit of the battery opened, so as to permit thedrops to be replaced.By the use, therefore, of my invention, the supervising operator cankeep a check upon the operations of the switchmen, and the appearance ofthe disconnecting-switch furnishes a complete indicator of the conditionof the main switch-board. If all his plugs 1" remain on the top bar, It,the operator knows that no substation lines are interconnected. If, whenthe plugs are so disposed, one or more of the annunciator-drops 0 fall,it becomes evident that one or more subscribers lines are connected oneach of the cross-strips of the main board corresponding to the dropsthat fall. If he desires to listen, and thereby supervise and assist theconversation, he may do so by placing the proper plug 1" on the thirdstrip, m. If he sees the plug 1* located on the second strip, l, heknows that the conversation is fully under way and that the twosub-station lines may, by giving a signal, cause his drop 0 to fall, andthus intimate their desire for-disconnection or for reconnection withsome other line. If the plug 1' is on the fourth strip and thecorresponding drop refuses to be replaced, he is aware that, though theconversation is finished and he has given the order to disconnect, thedisconnection has not yet been attended to by the switchman. It, on thecontrary, when the plug is on the fourth strip, he finds that the dropmay be replaced, he becomes aware that the circuits have beendisconnected from one another, and avails himself of the information toreplace the plug r on the top bar once more.

In the operation of my improved system it will be understood that I mayemploy as many horizontal connecting-strips in the main switch as I findnecessary, provided that I connect with each one an annunciator and avertical strip in the disconnecting-switch A. I may also, it'I prefer,group the horizontal strips a I) 0, when they become sufficientlynumerous, placing, for example, the six uppermost strips in one group,designating that group as group A, and the individual strips of thegroup A A and so on. The next group would be known as B, andwouldbesimilarly numbered. In the event of such a system of grouping, thereceiving operator-would designate the precise strip of any group withwhich any two circuits would be connected. I have operated the system asfollows: A receiving operatoris seated at the receiving-table E, aswitchman at the main switch B, and a supervising operator at thedisconnecting-switch A. A substation, we will say, No. 29, desires toconverse with No. 35, and transmits the call-signal in a manner wellunderstood. The annunciatordrop 0 on the line L, connecting with 29,falls upon the anvil t, and thus, by means of the derived circuit v, thedrop 0, and anvil t, causes an audible signal or buzz on the buzzer V.The operator presses the key, thus bringing her telephones into thederived circuit and receives the order, connect 29 with 35. She repeatsthe order and at the end of the repetition designates where theconnection should go on the main board. Thus 29 with on a,or, it'thestrips were numerous and grouped, 29 with 35 on A. This repetitionserves both to notify the subscriber that his call is correctlyunderstood and to indicate to the switchman on what strip to place thetwo lines. I use the buzzer V for convenience as a signal to thereceiving operator; but I do not restrict myself to its use, as I may,if I so elect, cut it out by a switch, so that the receiving-telephonemay be always in the derived circuit, and in that case the operatorwould be required to listen constantly for calls. The entire duty of thereceiving operator is to receive calls and designate the switch-stripupon which the several circuits are to be placed. The switchman standsbefore the main switch 13, and when he hears the operator repeat any twonumbers and conclude the repetition with the number of a switch-strip,he changes the plugs accordingly. The operator has now called 29 with 35on a, and the switchman therefore takes the plug 1' of vertical strip 1,connecting with 29, from its normal position just above the annunciator,and places it at the point where 1 intersects a. He also removes theplug of line 2, connecting with 35, to the same strip a, and by so doingthe two lines are connected together through the metal strip a, thenormal connection with the respective annunciators and ground plate isbroken, and as by the contact of the strip a with the two lines thegenerator-circuit is also closed the annunciator 0 at the disconnect-ITO ing-switch drops, and the supervising operator is thus apprised thataconnection has been made between two line-circuits, the substation bellat both stations being simultaneously rung by the current from theelectrical generator M, which flows over each line from the moment ofconnection. The connection is now in charge of the supervising operatorat the disconnecting-switch A.

As hereinbefore indicated, the plugs r are on the top or generator bar,70. When, now, by means of the generator-circuit closing through thedrop 0 to the two connected lines, the said drop falls the supervisingoperator allows the plug r to remain for a short time on thegenerator-strip 76, so that both lines will be signaled35 that hisattention may be attracted and 29 that he may know that 35 is called. Hethen slides the plug 0" down to the telephone-strip m to see that thetwo subscribers are properly connected, and that they commence theconversation. The plug is then placed upon the ground-strip l, where itremains as long as the subscribers are talking, so that they may bealways connected through an annunciator with the central station. Asignal from either of the two connected lines now once more drops theannunciator o, whereupon the operator slides the plug again to thetelephone-strip m to see what is wanted, thus enabling the subscriber tosignify his desire for disconnection or to be connected with a secondline.

The operator constantly occupies himself by sliding the plug down ontothe listening-strip to ascertain whether persons are talking or not.WVhen he thus ascertains that the subscribers have finished theirconversation he slides the plug 1" down to the battery-strip, and ordersthe switchman to disconnect the circuits. In practice I have done thisby tickets having the designated strip printed thereon. The ticket beingpassed to the switchman, his duty is at once to disconnect both.

circuits and restore their normal connections, after which he forwardsthe same ticket to the receiving operator, or otherwise informs her thatthe strip a is clear and ready for another connection. The drop 0,influenced by the battery K, will not be held up by its armature untilboth circuits are disconnected, and as soon as the supervising operatorascertains that the two circuits are disconnected by his ability to putup the drop he returns the plug 0* to the top or generator strip, and isready for another call upon that strip.

Having thus specifically described my invention and its application, Iclaim- 1. Thecombination,in atelephone-exchange, of a main switch-board,a series of main lines connected therewith, a series of annunciators,one for each line, a receiving-table provided with telephones and alarmdevices, connecting devices between the annunciators and thereceiving-table, whereby when a signal is received over any main linethe receiving-table is automatically connected with said line, and anauxiliary switch-board permanently connected, as indicated, with themain switchboard, whereby any two lines connected together upon the mainswitch-board may be supervised by an operator at the auxiliary board,irrespective of the distance between the said main and auxiliaryswitch-boards.

2. In a telephone-exchan ge system, the combination, substantially ashereinbefore set forth, ofa main switch-board adapted for the receptionofa series of main lines, and an auxiliary switch-board, the verticalconductingbars of the latter being each connected through theelectro-inagnet of an annunciator with a corresponding connection-barot' the main switch, whereby when any two main circuits are connectedtogether upon any connection bar or strip of the main switch-board, abranch circuit is established through the auxiliary switch-board, forthe purposes specified.

3. In a telephone-exchange system, the combination, with a series ofmain lines extending to sub-stations and a main switch-board therefor,of an auxiliary switch provided with a calling-generator, receiving andtransmitting telephones,.a steady battery, and a groundwire, each inseparate branch circuits, and having its vertical strips connected bywires with the horizontal strips of the main switch, whereby when one ormore line-circuits are connected with a connection-strip, thecorrespondin g vertical strip of the auxiliary switch with that one ofthe four branches to which it is plugged becomes a terminal of the saidline circuit or circuits, as and for the purposes specified.

4. A main switch-board having its vertical conducting-bars connectedwith a series of main lines, combined with an auxiliary switchboardwhose vertical strips or bars are permanently connected each with acorresponding horizontal connecting-strip of the main switch, and havingits horizontal bars or strips severally connected, one with anelectrical generator, one with the earth direct, one with receiving andtransmitting telephones, and one with a steady battery, substantially asdescribed.

5. In a telephone-exchange, an auxiliary or disconnecting switch-boardhaving its vertical conducting-strips connected through a series ofannunciator-magnets with the connectingstrips of a main switch-board andits horizontal conducting-strips severally connected permanently to anelectrical generator for signalin g purposes, transmitting and receivingtelephones, a constant battery, and a ground-wire, substantially as andfor the purposesspecified.

6. The combination, with an annnnciator normally connected in themain-line circuit between the inain line and the ground terminalthereof, of a normally-open derived circuit consisting of the metallicbase and drop or shutter of said annunciator, a wire connecting the samewith the main circuit at a point on the line side of the annunciator,and a metallic support or anvil common to a series of annunciators andpermanently connected through a signaling-instrument or one or moretelephones to earth, whereby when a call-signalis received and theannunciator-drop falls upon the metal support the derived circuit,including the receiving-instrumcnts, is automatically establishedwithout breaking the original circuit through the annunciator to earth,as described.

7. The combination, with a main circuit to earth,including anannunciator-helix, ofa normally-open derived circuit comprising themetallic frame and drop of said annunciator, a wire connecting the samewith the main circuit, and a contact-bar connected to earth through areceiving-instrument, the said normally-open circuit being adapted toclose antomatically upon the reception of a call-signal by means of thecontact between the drop and the contact-bar, independent of theoriginal circuit through the annunciator to each, which remains intact.

8. As a means of automatically and simultaneously signaling any twosub-stations located on ditl'erent main lines, the combination, in asystem of electric switching and signaling, of a series ofconnection-strips, each adapted to temporarily unite any two main lines,and an electrical generator common to the series and normally inelectrical connection with each and every connection-strip of the saidseries, substantially as described.

9. As a means of automatically signaling any two sub-stations located ondifl'erent lines in a telephone-exchange system, the combinationofaseries of connection-strips in a switchboard with a generator orsource of electricity, having one pole or electrode connected with theearth and the other or complementary pole normally connecting by meansof branch wires with all or a part of the said series ofconnection-strips, substantially as specified.

10. In a telephone-exchange system, a series of sub-station lines,switch deviees,suhstantially as indicated, for the directinterconnection of any two of said lines, and auxiliary devices combinedtherewith for the simultaneous establishment from a point at or near thejunction between the said twolines of abranch circuit extending to anauxiliary switch and normally connected thereat with an operativeelectrical generator, whereby the act, of connecting two lines togetheris caused to automatically signal the stations located thereon, buttransferable at will from the said generator to a telephone, a constantbattery, or a direct ground-wire, substantially as specified.

11. In a telephone-exchange system, a series of main lines, a mainswitch-board therefor, an auxiliary switch-board having each of itsvertical strips connected electrically with a connecting-strip of themain switch, and an annunciator included in the circuit of thecnmeeting-wire between the said main and auxiliary switches, combinedwith an electrical generator permanently connected with one of thehorizontal strips of the auxiliary switchboard to which the verticalstrips are all no mally plugged, whereby when one or more main lines areconnected together on any main switch-connecting strip thegenerator-circuit is closed and a signal automatically transmitted tothe sub-stations of each line so connected, and the annunciator of theauxiliary switch caused simultaneously to drop and indicate that aconnection is made, substantially as hereinbefore described.

12. A series of main lines, a main switchboard therefor, and anauxiliary switch-board connected, as described,with the mainswitchboard, in combination with an annunciator conneeted in circuitbetween the two switchboards, a telephone or telephones, a key orswitch, and wires connecting the said key and the telephones with one ofthe horizontal strips of the auxiliary switch-board, whereby when thesaid horizontal strip is connected with any two subscribers lines bybeing plugged to a vertical stripin contact with such lines conversationmaybe listened to or either substation spoken with without disturbingthe communication between the said two lines, as specified.

13. The combination, substantially as described, of a switch-boardconnecting-strip, a key or switch permanently connected therewith, atelephone or telephones in a branch circuit to earth and normallyconnected by the back limit or bridge of said key with the key andswitch-board strip, and a branch wire from an electric generatorterminating in a front contact or anvil for said key, whereby the saidkey when pressed is adapted to transiently sever its normal contact witha telephone and form a new contact with the generator, for the purposesspecified.

14:. In a telephone-exchange system, a series of main lines, a mainswitch-board'thcret'or, and an auxiliary switchboard connected in themanner described with the main switch-board, in combination with anannunciator connected in circuit between the twoswitch-boards, and aground-wire permanently attached to one of the horizontalconducting-strips of the auxiliary switch-board, whereby when any twosubstation lines are connected together and the vertical strip of theauxiliary switch corr sponding to the connection-strip in use is pluggedto the said grounded strip the connection of the central station withthe sub-station lines is constantly maintained withoutintert'ering withthe communication of the connected lines.

15. The combination, substantially as hereinbefore described, of amainswitch-board, an auxiliary switchboard, wires connecting the horizontalconducting-bars of the main switch with the vertical conducting-bars ofthe auxiliary switch, and an annunciator-helix ar- ICC ranged betweenthe said switch-boards in the circuit of the said conductin g-wires,forthe purposes specified.

16. The combination, substantially as here- 5 inbefore set forth, of aseries of main lines, a

switch-board whereby any two of the same can be placed in directcommunication one with another, and an auxiliary switch-board adaptedfor the convenient supervision of the same 10 when so connected with anannunciator, and

a constant battery connected on one side with the earth and on the otherwith one of the horizontal conducting-strips of the auxiliary switch,whereby when any vertical strip form-

